The invention relates to a crusher comprising a main shaft, which is placed into a bore of a rotatable eccentric shaft, the main shaft having a central axis which is inclined with respect to the axis of rotation of the eccentric shaft, and a first crushing head, which is attached to the main shaft and rotatable by the main shaft with respect to a second crushing head so that constrained stroke motion is effected between the first crushing head and the second crushing head, whereby material can be crushed between the first crushing head and the second crushing head, whereby the eccentric shaft comprises an outer eccentric shaft with a second bore and an inner eccentric shaft, which is at least partly positioned so as to be continuously turnable with respect to the outer eccentric shaft in said second bore, whereby the bore is in the inner eccentric shaft, and whereby the inner eccentric shaft and the outer eccentric shaft are turnable with respect to each other by means of gear transmission so that the inclination of the central axis of the main shaft changes with respect to the axis of rotation of the eccentric shaft such that the length of the constrained stroke motion changes.
An arrangement for adjusting the value of constrained pendulous motion or stroke of a crusher is previously known, in which an eccentric shaft is carried by an eccentric bearing having a wedge groove on the outer surface of the eccentric bearing. The eccentric bearing is held in place by means of a corresponding safety wedge so that the bearing cannot rotate during the rotating motion of the eccentric shaft. By turning the eccentric bearing, the stroke can be adjusted. In this crusher, the stroke is adjusted stepwise.
Another known method for adjusting stroke of a crusher having an eccentric bearing is to replace the entire eccentric bearing with a different kind of eccentric bearing providing a different stroke.
In the aforementioned arrangements, the stroke adjustment always requires dismantling of the crusher.
A solution to this problem is described in U.S. Pat. No. 5,718,391. This publication discloses a stroke adjusting apparatus, wherein an outer eccentric shaft comprises a worm shaft turnable by means of a hydraulic motor, the worm shaft being arranged to co-operate with toothing on the outer surface of the inner eccentric shaft such that the inner eccentric shaft can be turned in the outer eccentric shaft. This arrangement thus allows the stroke adjustment to be made without having to dismantle the crusher. A disadvantage of this solution is, however, that the worm gear and hydraulic motor required for turning the eccentric shafts with respect to each other are machine elements that require a lot of space. Thus, the eccentric shaft and thereby the crusher frame have to be sized much bigger than would otherwise be necessary. Accordingly, the total weight of the crusher and its manufacturing costs increase considerably.
Furthermore, the crusher disclosed in U.S. Pat. No. 5,718,391 has the problem that the hydraulic fluid required for effecting the stroke adjustment of the crusher has to be distributed through the outer eccentric shaft in rotating motion to the hydraulic motor while the crusher is in operation. Under dusty conditions of a crushing plant it is very difficult to make this kind of arrangement such that it does not leak.
The invention relates to a crusher which solves the problems described above. The crusher according to the invention is characterized in that the gear transmission comprises a first cog wheel attached to the inner eccentric shaft, a second cog wheel attached to the outer eccentric shaft, and a turning mechanism for turning the first cog wheel and the second cog wheel with respect to each other such that the inner eccentric shaft and the outer eccentric shaft turn with respect to each other.
Thus, the internal stroke adjustment arrangement of the crusher is entirely mechanical in the solution according to the invention.
The preferred embodiments of the crusher according to the invention are disclosed in the dependent claims.
The invention is based on the eccentric shaft comprising two parts, the outer eccentric shaft and the inner eccentric shaft inside it. The first cog wheel is attached to the inner eccentric shaft and the second cog wheel is attached to the outer eccentric shaft. By turning the first cog wheel and the second cog wheel with respect to each other by means of the turning mechanism, the inner eccentric shaft and the outer eccentric shaft turn with respect to each other.
With this arrangement the inclination of the central axis of the main shaft can be changed with respect to the axis of rotation of the eccentric shaft such that the value of the constrained pendulous motion, i.e., the stroke, changes.
The crusher according to the invention provides the advantage that the stroke can be adjusted without dismantling the crusher. The arrangement according to the invention also enables a continuous stroke adjustment within a range of 0 to 40 mm, for example.